Thermally Induced Changes in the Chemical and Mechanical Properties of Epoxy Foam

The influence of thermal treatment on the chemistry, physical, and mechanical properties of epoxy foam was evaluated. The foam was subjected to repeated thermal cycles (25-958 degrees C), encompassing the temperature regime in which the forward and the retro Diels-Alder reaction occurs. Changes in the chemistry of the foam were evaluated using in situ FTIR spectroscopy during thermal exposure. In addition, the structural siloxane units within the epoxy foam were identified and evaluated using FTIR analysis. Thermal analysis was used to evaluate expansion, degradation, and mass loss during thermal exposure. Finally, the physical and mechanical properties were evaluated to determine how thermal cycling influences the density and modulus of the epoxy foam. Thermal exposure below the temperature required for the breakage of conjugated double bonds via Diels-Alder mechanism increases thermal expansion influencing the structural integrity and packing of siloxane chains. The data indicates that the chemical changes and the thermal expansion of the foam are irreversible. The combination of thermal expansion and the change in chemistry for the system strongly diminished the structural rigidity of the foam lowering the density and modulus of the material.